ORLANDO, Fla. --  A 21-hour standoff ended with an Orlando man killing four children and turning the gun on himself, police said. 

Law enforcement entered the apartment near Universal Orlando on Monday night to find Gary Wayne Lindsey Jr. dead in a closet from a self-inflicted gunshot wound and all four children he was holding hostage dead from apparent gunshot wounds.

It's undetermined exactly when Lindsey, 35, killed the 1-, 6-, 10- and 11-year-old children, Orlando Police Chief John Mina said.

He added that the Medical Examiner as well as crime scene investigators are working to pinpoint a time of death for the children throughout the standoff.

Lindsey is also accused of shooting Orlando Police Officer Kevin Valencia, who remains in critical condition at Orlando Regional Medical Center, after he responded to the apartment over a domestic violence call late Sunday night.

Valencia has two children ages 5 and 8 months, police said. An online crowdfunding page has been set up for Valencia and his family, and the donations, which are tax-deductible, will be collected by the Orlando Police Heroes Foundation, police said. 

"Our No. 1 priority right now is the health and well being of Kevin Valencia and our officers who had to see this tragedy," Mina said Tuesday.

Children found dead

A tarp now covers windows of the second-floor unit of the apartment at the Westbrook Apartments off Kirkman Road and Florida's Turnpike.

Mina said officers were in continual contact with Lindsey, and throughout the standoff, there never was an indication of an imminent threat to the children.

Lindsey had a spotty Wi-Fi connection, so officers decided to try to get him one of their own phones so they could keep in better touch with him, to no avail.

“You could hear them negotiating, asking him, ‘Hey, could we at least get this child?’ Gary, we have a phone by the door. Will you at least come to the door? We don’t want anybody to die,”​ said neighbor Tannish Laws. 

Around 6 p.m. Monday, Orlando Police SWAT teams were replaced with SWAT teams from the Orange County Sheriff's Office. 

At about 8:30 p.m., an officer who went to deliver a phone to the apartment saw that one of the children was visibly dead.

That's when Mina said they decided to go in with the SWAT team. At about 9 p.m., neighbors heard a loud boom, which turned out to be officers making a forced entrance into the apartment.

When they went inside they found the bodies of the children. Two were in one bedroom, two in another. All appeared to be dead of gunshot wounds, Mina said. Lindsey's body was found in a closet, along with a gun.

Two children were Lindsey's; the other two were related to the woman who fled the apartment during the initial domestic violence call. Mina said it's still unclear when the children died.

Lindsey was found to have two rifles, two shotguns and a handgun in the home, which investigators think Lindsey, a convicted felon, acquired from his now-deceased father.

"We continue to ask for thoughts and prayers (for Valencia)," Mina said. "The next several days will be very telling on his condition."

Gary Wayne Lindsey Jr. (Volusia County Sheriff's Office)

Initial domestic violence call

The incident started with a domestic violence call to police at about 11:45 p.m. Sunday.

When officers arrived at the scene, a woman met them away from the apartment unit at the complex's community room and told them that her boyfriend had battered her.

When officers approached the apartment, the man inside, who Mina said was Lindsey, opened fire.

Valencia was struck and rushed to ORMC. Mina wouldn't specify the nature of Valencia's injuries but said they're "very severe. He's in critical condition." Valencia is in his 20s and has been with the force for about two years.

An online crowdfunding page set up by the attorney representing the woman's family identified the children as Irayan, 12; Lillia, 10; Aidan, 6; and Dove, 1; and the woman as Ciara.

Family, community mourns

Stuck into the chain link fence, a small memorial is growing for the Lopez children at the Westbrook apartments.

Neighbor and family friend Nicole Gonzalez says she can’t believe how the last 48 hours have played out.

"You can see the love that they had for each other … they had their whole lives ahead of them," Gonzalez said. "I am heartbroken … because the worst possible outcome is what happened."

Walter Benenati, the family's attorney, said that Irayan loved video games and school, that Lillia loved Volcano Bay and attended Sadler Elementary, and Aidan loved dinosaurs and to play.

"(The family is) certainly grieving -- complete and utter shock of what has occurred. And it’s just an unspeakable act," Benenati said.

The family wants more awareness brought to mental health and domestic violence.

"Our thoughts and prayers go with the law enforcement officer that almost had his life taken. And right now the family is not really looking at the protocol of what occurred or how it occurred. Right now, they are grieving and that is for another day," Benenati said.

According to authorities, there will be a review to see what they can learned from this tragedy. 

Spectrum News' Bailey Myers, Greg Angel, Deborah Souverain, Erin Murray and Audrea Huff contributed to this report.

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.