ORLANDO, Fla. -- The four children killed by a gunman during a 21-hour standoff are thought to have been shot dead in their beds while they slept, Orlando Police said Thursday.

The children -- Irayan, 12; Lillia, 10; Aidan, 6; and Dove, 1 -- were found dead in their respective beds wearing the same bedtime clothes they were dressed in when their mother put them to bed, investigators said.

The mother, Ciara Lopez, called law enforcement Sunday night to report that her boyfriend had battered her. The boyfriend -- Gary Wayne Lindsey Jr. -- then holed up in their apartment with the four children inside.

Investigators think the children were killed either shortly before or shortly after Lindsey's initial contact with Orlando Police officers. They were all shot with a single handgun that Lindsey, a convicted felon, had stolen from his father, police said.

Officer still fighting for his life

Orlando Police Ofc. Kevin Valencia (Orlando Police)

Ofc. Kevin Valencia, an Orlando Police officer who was one of the first officers to approach the apartment after police were dispatched, was shot and remained in critical condition in a coma Thursday.

Surgeons at Orlando Regional Medical Center said he's shown some signs of responsiveness.

His wife, Meghan, said at a news conference Wednesday that Valencia is fighting for his life just as he fought for others. 

"He is fighting every second and I need him to continue to keep fighting," said Meghan Valencia through tears.

Accused gunman's past

Lindsey was a convicted felon on probation and was not legally allowed to have a firearm.

His criminal history began in 2008, when he got into a fight with his girlfriend at the time and received 10 years' probation for that.

Ciara Lopez, the mother of the children, applied for a protective order from Lindsey at one point. But she didn't show up in court, so the judge refused to grant it.

Just a few weeks ago, investigators say Lindsey violated his probation in Seminole County by stealing hundreds of dollars' worth of merchandise from a Walmart.

But Lindsey didn't serve jail time, because his probation officer said his actions did not indicate he was a threat to the community. 

Costly recovery

Online crowdfunding pages have been set up for officer Kevin Valencia and his family, who face a long road ahead, and the family of the mother of two of the children killed in the standoff. The GoFundMe pages listed above are not managed by Spectrum News. For more information on how the site works and the rules, visit http://www.gofundme.com/safety.