While holding a gun to his 2-year-old son’s head, Thy Ho told his girlfriend and her teenage son he would shoot them all and then himself, Gwinnett County police said Thursday.

“I’m ready to die tonight,” Ho said.

Less than 24 hours later, both the boy and his father were dead. After a 19-hour standoff with officers, Ho shot his son and himself Wednesday afternoon inside their Buford home, according to police. His girlfriend, Huyen Nguyen, and her 15-year-old son were released unharmed.

On Thursday, Gwinnett police presented a timeline of events, which started with a Tuesday night argument between Ho and Nguyen. But there were no answers to the biggest question: What would lead a father to kill his own son?

Since October 2013, officers had been called four times to the Beyers Landing Drive home that Ho, a convicted felon with criminal records in Georgia and Indiana, shared with his girlfriend, according to police. No arrests were ever made, said Cpl. Deon Washington.

Investigators have not determined what led to their last argument Tuesday night. But, shortly before 10 p.m., Nguyen’s son called his 20-year-old sister and said Ho had a handgun and was refusing to allow anyone to leave. She called 911 as she drove to the home.

“I don’t feel like they’re going to be safe with him around,” the woman told the operator. “He’s got a history of violence.”

After officers arrived, Ho let the Nguyen and the teenager leave, but not the couple’s toddler, Phillip, Washington said.

Neighbor JoAnn Mason said she watched as officers lined the street and listened to the officers broadcast their intentions to Ho.

“We could hear them say, ‘We are the Gwinnett County Police. We’re not going to leave. We’re here for your safety. Put down the gun and come out with your hands up,’” Mason said. “We heard it over and over, maybe 25 times.”

But Ho ignored those orders. For hours, Ho communicated sporadically with SWAT negotiators, positioned outside the home, through calls and texts, according to police. Ho asked to speak to Nguyen, but officers declined, Washington said.

At 3 a.m. Wednesday, Ho’s parents were brought to the home, but he still refused to surrender. Ho texted a picture of himself and the boy in bed, and the toddler was asleep, police said. Officers entered the home, but not the master bedroom.

Gwinnett police asked for assistance from DeKalb County police, whose SWAT team arrived and took over. Nearby streets remained blocked off, preventing residents from coming or going, even to school or work.

At 4:34 p.m., Ho fired a shot through the master bedroom door toward officers, Washington said. Seconds later, two more shots were fired. Officers rushed into the bedroom to find both the boy and Ho with gunshot wounds. Neighbors watched as an officer raced the boy outside to a waiting helicopter.

“We saw when they brought him out and his arms were limp and his eyes were closed,” Mason said. “That broke my heart.”

Ho was also brought outside and loaded into an ambulance. Police said late Wednesday that neither Ho nor his son survived.

Mason praised the officers’ work, but said she is convinced Ho knew how he wanted the stand-off to end from the beginning.

“I can’t figure out, as a mother and a grandmother,” she said, tearing up, “how anybody could want to hurt their child.”