An 18-year-old man found naked in an Arlington pool last week where a teenaged mother and toddler died has been charged with two counts of murder.

Homicide detectives arrested Andrew Michael Gomez late Saturday night after he was interviewed by detectives. Police said he admitted drowning longtime friend Tiffany Cecconi, 18, and her daughter, 18-month-old Kaylani.

"He was in the pool with the two bodies when the grandmother found the grandchild and her daughter the 18-year-old," Lt. Larry Schmitt told reporters Sunday, stopping short of laying out any specific evidence. "I'm not going to get into all of the details of the investigation. But we were able to gather enough evidence to find probable cause to believe he murdered both of them."

According to police reports obtained by Channel 4, Gomez told police he went to the pool of The Cove subdivision with Cecconi -- a longtime friend -- and her daughter about midday Wednesday and that they were the only people there.

He told police he went into the pool holding Kaylani while the mother was sitting off to the side. Police reports said Gomez started moving Kaylani around in his arms in a manner that upset the toddler and she told him to stop.

At this point, the reports said Gomez claimed Cecconi got into the pool and tried to get Kaylani away from him. Gomez said he started fighting with Cecconi with one hand, while still holding the toddler with the other.

"The suspect said that during the fight he dropped the baby in the pool. He continued fighting Tiffany with both hands," the report says.

Investigators specifically asked Gomez if he killed Cecconi and he said he did, though he did not remember holding her under water, the report said.

Police said Gomez told them after the fight, he simply stood in the water and did not help Kaylani, who was still in the pool. He said he didn't know why he didn't help the young girl.

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On the day of the drowning, the man who originally called 911 said a man family members said was Gomez was just standing there, naked and not acknowledging anyone, including rescuers and police. The man said rescuers had to pull him out of the pool, not because he was drowning but because he appeared to be in a trance.

"Something just didn't seem right," said the man who chose to remain unidentified. "Why was he naked in a pool while she was at the bottom?"

"From what I saw, I don't think it could be a drowning," the man added. "How could two people drown when one person who was completely conscious was there?"

The police report said it appeared to arriving rescuers that Gomez ingested a large amount of pool water. He remained hospitalized at Shands-Jacksonville Medical Center in stable condition on Sunday.