Jennifer Clarey was a doting mother, neighbors say, who invited kids on the block to play with her toddler son, planted flowers in her yard in Bucks County, and recently threw a party for her child's second birthday.

What appeared to be an idyllic life became a tragedy late last month: Clarey's 2-year-old son, Mazikeen Curtis, was found dead in bed Aug. 25 at their home on Lovett Avenue in Tullytown. Authorities alleged Tuesday that Clarey, 42, had deliberately mixed a lethal dose of children's Benadryl and the powerfully addictive prescription opioid, hydrocodone, in Mazikeen's sippy cup. She later cut her own wrists but survived.

Clarey has been charged with criminal homicide, a broadly defined crime that spans involuntary manslaughter to intentional killing. She is the only suspect, officials have said.

An empty 120-pill bottle of hydrocodone, prescribed to Clarey and filled on Aug. 18 was found at the scene, according to a criminal complaint. It had been kept in a locked strongbox. An empty bottle of Children's Benadryl was also found at the scene, in the trash. Officials have also said it was unlikely that Mazikeen, who turned 2 on July 15, opened and ingested the bottles of Benadryl and hydrocodone by himself.

"We are treating it as a first-degree murder case," Deputy District Attorney Matthew S. Lannetti said Wednesday.

Lannetti said he didn't know why Clarey, who has an adult child, had been prescribed hydrocodone.

Authorities on Wednesday said they still did not have a motive for the killing.

Neighbors, too, couldn't begin to guess what would have prompted a mother to kill her own child.

"He seemed like a happy, healthy baby. He never seemed like he was in danger," said Kennidi Hollander, a neighbor whose 2-year-old daughter often scribbled with chalk alongside Mazikeen. "He was incredibly smart."

Hollander said Clarey and Clarey's boyfriend began renting the Lovett Avenue house in January or February.

The boyfriend, who is not Mazikeen's father, stopped living at the house several weeks ago, Hollander said, after he complained to her that Clarey would disappear from home for hours, leaving Mazikeen in his care and not responding to calls or text messages.

"I mean, how can you accidentally get drugs into a kid's sippy cup?" said neighbor Staci Winters, Hollander's mother. "You can't accidentally do it."

"I can't even wrap my head around this at all," Winters said of Mazikeen's death, sitting on a couch at her house. "I really don't understand it."

In 2012, Clarey pleaded guilty to possession of drug paraphernalia, in addition to retail theft. In 2014, according to state court records, she was found guilty of a number of motor vehicle offenses, including failure to carry a license and registration, speeding in a school zone, and driving with a revoked license.

Public records show Clarey had been evicted from numerous Bucks County apartments over the last 15 years before she moved to Tullytown, where, by neighbors' accounts, she seemed to work hard to be an attentive mother.

"My daughter and my granddaughter, they were outside playing with her all the time," Winters said. "Every time I looked outside, she was outside."

Now, the exterior of Clarey's home has balloons and teddy bears tied to a chain-link fence in the front yard. A picture of Mazikeen is fastened to the gate.

"Even now, knowing what I know, I would do nothing in the world to help her," Winters said. "I feel repulsed by her now."