Before he brutally killed his girlfriend in front of her children two years ago in Pennsylvania, Danelo Souza Cavalcante seemed like a positive match -- a fellow Brazilian who was a good neighbor and kind -- the girlfriend's sister says.

But Cavalcante, now the subject of a manhunt after he escaped from a Pennsylvania prison last week, seemed to transform over time, eventually exuding jealousy and threatening Deborah Brandão before her death, her sister told CNN.

Now the sister, Sarah Brandão, who lived near both of them and is taking care of Deborah's two children and well as her own daughter in Pennsylvania, is terrified about his escape and worried that he could come after her.

"I haven't slept for many days. Since (his escape) I have been waking up with fright at night. I nap and wake up with fright," Sarah Brandão told CNN in an interview translated from Portuguese to English.

Cavalcante, 34, who was convicted just last month of first-degree murder in Deborah Brandão's 2021 killing, escaped from the Chester County Prison some 30 miles west of Philadelphia on August 31, sparking a search involving hundreds of officers.

Cavalcante, who also is wanted in a 2017 homicide case in Brazil, is extremely dangerous and desperate not to get caught, authorities have said, and they've urged residents in areas near the prison to keep their doors locked, stay inside, and check their security cameras.

He changed from a nice neighbor to a jealous boyfriend, sister says

Deborah first met Cavalcante because they were neighbors in Chester County, Sarah told CNN. He helped and was kind to Deborah, she said.

They dated for about a year and a half, according to Sarah.

"She said he was nice to her, he was nice to her children, that he helped her," Sarah told CNN. "He kept her company. She didn't feel alone anymore."

"He seemed normal, but he was always very silent, observant and reserved," she added.

He treated Deborah's two children well, but "there wasn't much attachment to them -- no love, no hug, nothing; very cold," Sarah said.

His behavior toward Deborah changed over time, Sarah said.

"She kept saying that he was extremely jealous -- that when he drank, he became a different person; that he kept going through her cell phone," Sarah said.

Cavalcante would threaten Deborah, telling her he would "do the worst" to her if she ever cheated, Sarah said.

Cavalcante killed Deborah, 33, in April 2021 by stabbing her 38 times in front of her then 7- and 4-year-old children, the Chester County district attorney's office has said. She had filed a protection from abuse order against him the year prior, according to a probable cause affidavit.

Just days after his conviction last month, Cavalcante was sentenced to life in prison without the possibility of parole.

Sister fears fugitive will show up at her home

When Cavalcante was sentenced last month, Sarah felt relief. Deborah was honored and received justice, she said.

But since Cavalcante's escape, Sarah has been living in fear, she told CNN.

"I was desperate, desperate, very scared. I thought about my children, obviously," Sarah said.

Sarah is worried Cavalcante could show up at her Chester County home and afraid he will come after her.

Despite her fears, she believes police will capture Cavalcante, she said.

Deborah had brought her children to the US for a better life, sister says

When Sarah learned about her sister's murder, "my world ended," Sarah told CNN.

The sisters were best friends, she said: The only time they weren't together was at bedtime.

"We worked together all day. We talked on the cell phone all day when we weren't together," Sarah said.

Deborah brought her children to the United States "because here the quality of life is better than in Brazil," Sarah said.

"She wanted to give a better life for both of them," Sarah said.

Now, Sarah is trying to give Deborah's children the lives her sister wanted for them, she said.

"I have a house cleaning company. My husband has a flooring services company. And we continue working our little life and trying to do the best for the children, which is what I have been doing since I lost my sister," she said.

"I try my best, right?"