FORT LAUDERDALE, Fla. -- A former Marine sharpshooter accused of invading the home of apparent strangers in Florida and fatally shooting a woman, her 3-month-old baby and two others was ordered held without bail during his first court appearance Monday.

Authorities did not give a motive for the grisly attack, but they said Bryan Riley may have a mental illness and he told investigators said he was high on methamphetamines at the time. His girlfriend said had been saying for weeks he could communicate directly with God.

At this court appearance Monday, Riley, 33, said he intended to hire a lawyer, but one will be appointed for him in the meantime.

Riley surrendered Sunday morning after a furious gunbattle with authorities who brought in at least one armored vehicle during their standoff. After it was over, an officer rushed into the home and rescued an 11-year-old girl, who was still conscious despite being shot seven times. She was in critical condition Monday, the sheriff's office said.

According to Polk County Sheriff Grady Judd, Riley told interrogators the victims "begged for their lives, and I killed them anyway."

Judd said Riley told detectives, "You know why I did this." But Brian Haas, the local prosecutor, said investigators don't.

"The big question that all of us has is, 'Why?'" Haas said. "We will not know today or maybe ever."

On Saturday evening, hours before the attack began, Riley stopped by the victims' home in Lakeland, about 30 miles from Tampa, where he lives, Judd said. Authorities have found no connection between Riley and the victims.

At the time, Justice Gleason, 40, was outside mowing his lawn, and Riley told him God had sent him there to prevent a suicide by someone named Amber. Gleason and another person Judd described as one of the victims told Riley no one by that name lived at the house and told him to leave. They called the police, but when authorities arrived, Riley was gone.

Riley returned around 4:30 a.m. Sunday, arranging glowsticks to create a path leading to the house in what Judd said may have been an attempt to draw officers "into an ambush."

Shooting began shortly thereafter -- and when an officer in the area heard popping noises, he sounded the alarm, bringing state and local law enforcement officers to the scene. When the first ones arrived, they found an apparently unarmed Riley outside, dressed in camouflage, and his truck ablaze.

But Riley then ran back into the house, where authorities heard more gunfire, "a woman scream and a baby whimper," Judd said.

Officers tried to enter the house, but the front door was barricaded. Judd said when they went around to the back, they saw Riley, who appeared to have on full body armor.

Riley and the officers exchanged heavy gunfire, with dozens "if not hundreds of rounds" fired, before Riley retreated back into the home, Judd said.

Everything fell silent, until a helicopter unit noticed Riley was coming out, the sheriff said. He had been shot once and was ready to surrender. Authorities did not say where he was shot.

Officers heard cries for help inside the home but were unsure whether there were additional shooters and feared the home was booby-trapped. Still, one officer rushed in and grabbed the wounded girl, who told authorities there were three dead people inside.

Officers sent robots into the home to check for explosives and other traps. They eventually found the bodies of Gleason; a 33-year-old woman; and her baby. The baby's 62-year-old grandmother was found in another home on the property. It's not clear when she was shot.

Authorities released only Gleason's name, and did not say whether or how he was related to the other victims, but on a Facebook page for a woman who identified herself as Gleason's girlfriend, friends posted comments lamenting her death. From the page, it was evident she recently had a baby.

Pansy Mincey Smith, who told The Ledger she went to school with Gleason's father, said the last time she saw the younger man he had just had a baby.

"RIP Justice Gleason. The last time I saw you, you were getting on the elevator at the hospital," Smith wrote on Facebook. "You were smiling from ear to ear about your new little baby boy, you had that big teddy bear for him. This is so heartbreaking, son."

The sheriff's office declined to say how many times the victims had been shot, but said they had all been huddling in fear, with the boy dying in his mother's arms. Even the family dog was shot to death.

Authorities said Riley's girlfriend told investigators he was never violent but had become increasingly erratic. She said he claimed to be on mission from God, stockpiling supplies for Hurricane Ida victims including $1,000 worth of cigars.

Riley's vehicle had also been stocked with bleeding control kits and other supplies for a gunfight, authorities said.

He worked as a private security guard and had no criminal history, the sheriff said.

"Prior to this morning, this guy was a war hero. He fought for his country in Afghanistan and Iraq," said Judd. "And this morning he's a cold-blooded killer."

While being treated at the hospital, Riley remained aggressive, at one point trying to grab an officer's gun. He was ultimately tied down and medicated.

Officers took Riley to jail in a white jumpsuit later Sunday. He appeared downcast, hanging his head and hardly opening his eyes, as reporters asked why he killed the family.

Associated Press reporter Kelli Kennedy contributed from Fort Lauderdale, Florida.