Mexican authorities arrested five more people on Friday in connection to the kidnappings of four Americans in Matamoros, Mexico, as the bodies of the two Americans killed were returned to US diplomats and questions continued to swirl around last week's violent abduction.
Six people have been arrested in total, including one on Tuesday, Tamaulipas Attorney General Irving Barrios Mojica said Friday.
"The Tamaulipas Attorney General's Office (FGJT) performed an arrest warrant against five people linked to the events of March 3 in Matamoros, for the crimes of aggravated kidnapping and intentional simple homicide," Barrios Mojica tweeted.
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"One more person who was arrested in recent days, was linked to the process."
The case remained "very confusing" to investigators, who were still obtaining information on last week's kidnapping and considering all angles, a Tamaulipas Prosecutor's Office official familiar with the investigation told CNN before news broke of the arrests.
Earlier, a cartel apologised for carrying out what one victim's father has called "a senseless crime" that also left one Mexican woman dead.
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An apology letter was issued Thursday by the Gulf Cartel, which is believed to be responsible for the kidnappings, and the group handed over five of its members to local authorities, according to images circulating online and a version of the letter obtained by CNN from an official familiar with the ongoing investigation.
CNN cannot confirm the authenticity of the photos and has asked Mexican and US authorities for comment.
Though investigators believe the letter to be authentic, Mexican and US law enforcement officials participating in the investigation strongly doubt the sincerity of the group's apology, the official who shared the letter with CNN said.
One person who has been detained was undertaking "surveillance functions of the victims," Tamaulipas Govenor Américo Villarreal said Tuesday, identifying the individual as 24-year-old Jose "N."
The Tamaulipas attorney general's office identified the person arrested Tuesday as Jose Guadalupe "G."
A judge ordered him to be temporarily detained for five months for the investigation to be carried out, the attorney general's office said.
Officials would not confirm whether the man has any affiliations with criminal organisations.
Meanwhile, the bodies of two Americans killed - Shaeed Woodard and Zindell Brown - were delivered to US diplomatic authorities on Thursday after undergoing forensic examination, Barrios Mojica said in a tweet.
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"I've tried to make sense out of it and tried to be strong about it," Woodard's father, James Woodard, told reporters Thursday, which would have been his son's 34th birthday.
"It just was a senseless crime."
The two survivors, LaTavia Washington McGee and Eric Williams, returned to the US Tuesday to be treated in a hospital.
Williams, who was shot three times in his legs, has since undergone two surgeries and had rods placed in his legs, his wife said on a GoFundMe page to raise money for Williams's medical and living expenses.
The mother of one of the survivors called for the arrests to continue.
"They need to keep getting them until they get them all," said Barbara Burgess, mother of Washington McGee, who was wounded during the ordeal.
Burgess added in a phone call that her daughter would be able to identify her attackers because of their tattoos.
The tight-knit group had travelled from South Carolina to Matamoros so that Washington McGee could undergo a medical procedure.
But the friends were violently intercepted by gunmen who fired into the Americans' van, roughly loaded them into the back of a truck and took them away, according to Burgess and a video of the encounter.
The victims were shuttled to multiple locations before they were found in a house around Matamoros Tuesday.
New video confirms Americans' route.
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Just after crossing the border and less than three hours before they were kidnapped, the four Americans were heading to a doctor's appointment they never showed up at, as seen in new livestream video taken by one of the victims and obtained, geolocated and analyzed by CNN.
CNN geolocated the video to a street in the northernmost section of Matamoros, located just off the off-ramp from the bridge the group used to cross into Mexico.
The clock on the GPS navigation, in addition to the length and direction of the shadows seen in the video, and the van's proximity to the bridge, indicate that it was taken a few minutes after 9.18 am, when the Tamaulipas attorney general says the group crossed into Mexico.
How the four ended up in that specific area, given its remote location and despite using GPS navigation, is unclear.
An analysis of the GPS routes seen in the video indicate that they were eventually traveling towards the doctor's office where Washington McGee had a scheduled appointment.
But CNN is told by a US official familiar with the investigation that the group never showed up to the doctor's office for that appointment.
The source also said the original appointment was for 7.30am but the group called the doctor's office and told them they were running late.
The video came from a Facebook Live by Williams.
CNN obtained it through a friend, who asked not to be named over concerns for their safety.
As the group drove south on Sixth Street in Matamoros, the driver then, contrary to the GPS navigation instructions, makes a right on Galeana Street, away from the doctor's office.
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Although the video is helpful in providing another timestamp of where the four were before they were kidnapped, it doesn't explain where they went for three hours instead of going to the scheduled doctor's appointment.
The next time the car is seen, according to the Tamaulipas attorney general, is on a surveillance video over a mile to the south of the doctor's office, at 11.12 am.
At some point, between 11.12 am and 11.38 am, a grey Volkswagen Jetta begins following the van, according to the Tamaulipas attorney general.
By 11.41 am, several vehicles are following the van. At 11.45 am, the cartel confronts the Americans and the shooting and kidnapping begins.
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López Obrador says investigation will be 'in depth'
The kidnappings have brought increased scrutiny on efforts to reign in cartel violence in Mexico, including from Republican lawmakers in the US who have called for designating cartels as terrorist organisations and signaled their plans to file legislation allowing the US military to operate in Mexico.
Republican pressure has been met with a swift rebuke from Mexican President Andrés Manuel López Obrador, who says the actions would infringe on Mexican sovereignty.
López Obrador said Friday the investigation will be "in-depth" and is an "important issue because the prestige of our country and of the government is at stake".
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He told reporters Mexican officials learned the Americans "had a criminal background in the United States," but he did not elaborate as to how that might relate to the kidnapping.
CNN is looking into the claims by the Mexican president regarding the four Americans' criminal history.
A US source told CNN the US hasn't uncovered any evidence the four Americans were in Mexico for criminal purposes.
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