Oklahoma Toddler Allegedly Murdered by Mother's Married Dentist Boyfriend: 5 Things to Know

In July, a 19-month-old Oklahoma boy died after authorities claim he was dropped on his head and kicked by his mother's then-boyfriend, a married dentist

In July, a 19-month-old Oklahoma boy died from injuries he’d sustained only days earlier, after authorities claim he was dropped on his head and kicked by his mother’s then-boyfriend, a married dentist with four kids.

Dr. Bert Franklin, the suspect, has pleaded not guilty to a first-degree murder charge in the death of Roxanne Randall’s son, Lincoln, court records show, and he remains behind bars without bond.

His attorneys did not return a message seeking comment.

Here are five things to know about the case.

1. Child’s Mom Was Home When He Was Allegedly Abused

Randall, Lincoln’s mother, was home in Tulsa, Oklahoma, at the time of his alleged abuse on July 16, but she told investigators she was upstairs.

She said she ran to her home’s basement when she heard a loud “thud,” but her boyfriend dismissed the noise.

According to medical examiners, Lincoln had sustained a skull fracture as well as brain bleeding.

A source close to Randall told PEOPLE last year that she knew something was wrong with her son the day after his alleged abuse, when he started having trouble breathing.

“He [Franklin] is not a human — he was eating pizza while this baby was unconscious,” the Randall source told PEOPLE, days after Lincoln died on July 18. “He’s a monster. He is absolutely a monster.”

2. Suspect Caught on Camera

Part of the alleged abuse was recorded by home surveillance cameras, authorities have said.

While the footage does not show the entire incident, Franklin can allegedly be seen kicking Lincoln — though his lawyers maintain he was kicking a dog — and, later in the video, while eating a slice of pizza, he can be seen cradling the boy, who appears limp.

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“There’s really nothing on the video that surprised me,” one of Franklin’s attorneys told a local TV station last year. “I mean it is what it is. And again, Dr. Franklin has told us there was a dog in there and any actions he had was towards the dog, and I believe him.”

Authorities further allege Franklin lied to Randall about the “thud” she said she heard. According to investigators, he told her he was throwing a ball to a dog and that Lincoln was fast asleep.

3. Franklin and Randall Dated for About a Year

The source previously told PEOPLE that Randall trusted Franklin with her son, noting the couple had been dating for nearly a year. Franklin even met Randall’s parents.

“Lincoln’s paternal grandmother and Lincoln’s father’s family adored Bert,” the source said.

“I can tell you nobody saw this coming,” the source added. “Not a single person. It’s just disgusting. Who would commit such a violent act?”

However, according to the source, Franklin led a double life during his relationship with Randall. “He had two Facebooks, for God’s sake,” the source said, noting he had blocked his wife and people she knew from one of his Facebook pages. “He was living a complete lie. Everything was lie.”

The source said Randall was led to believe Franklin had “legally separated from his wife and was going through a divorce.”

4. Child’s Mom Is Speaking Out

On Monday, Randall sat down on Dr. Phil to discuss the death of her son and the prosecution of her then-boyfriend.

In an exclusive clip from the interview, she described for host Phil McGraw the first moments she realized something was wrong with Lincoln after he’d allegedly been abused.

“I woke up at [2 a.m.] to a sound; I thought Lincoln was coughing,” she said. “I woke up, and I just remember instantly thinking, ‘Oh, I knew it’ — he was sick.”

Randall said she went to the kitchen to get Lincoln some medicine and his bottle, and when she returned the toddler was “gurgling.”

“I put the stuff down and I grabbed him. And when I grabbed him, his body was limp,” she said. “So I yelled at [Franklin] to call 911, and he stood up at the other side of the bed and just stared at me.”

5. Source: Lincoln Was ‘a Fighter’

Lincoln — who was born three months premature — was described by the Randall source as “a fighter.” The little boy endured months of emergency care before going through a number of surgeries and therapies, the source said.

“Lincoln was the happiest baby I have ever met,” the source said. “He never cried … he was just happy existing. As long as he could see somebody, he was happy.”

The source told PEOPLE that Randall had seen “Lincoln through a lot of medical issues, so for him to be taken out by a grown man like this is very sad. It’s very disheartening.”