Islamabad, Pakistan (CNN) The bereaved widower of a young Pakistani woman allegedly burned to death by her family says her relatives guaranteed her safety to persuade her to visit after she eloped against their wishes.

But after 18-year-old Zeenat Rafique arrived at her family's home in Lahore on Wednesday, her mother and brother tied her to a bed, poured gasoline and set her on fire, according to Punjab police representative Nabeela Ghazanfar.

An autopsy released Thursday said Rafique had traces of smoke in her respiratory tract, indicating she was alive when she was set ablaze, CNN affiliate Geo News reported.

Her mother, Parveen Rafique, has turned herself in to authorities and expressed no sorrow for her actions, police said. She's being held on suspicion of murder, while the brother, Ahmer Rafique, is on the run, police said.

Forbidden love

After Rafique was laid to rest Thursday, her tearful husband, Hassan Khan, 19, told CNN that the young lovers had been married only 11 days ago.

They spent three days together as husband and wife before her family persuaded her to return home temporarily, he said.

"Her relatives came and we told them that we're married now. They said, 'That's fine,' and asked us to send her home," he said.

"Her cousin gave the guarantee that nothing would happen to her. We were not sending her otherwise."

She was supposed to return Thursday but was killed the day before, he said.

"We went to her house, she was gone, she was finished and they had thrown her burnt body on the stairs," he said.

Allegations of earlier violence

Khan said his late wife's family had been violent toward her before over her wish to marry.

"The day we eloped she had been abused, there was blood on her nose and on her lips," he said. "She was in distress; she asked me to take her away and marry her."

He told police she had feared for her life after they eloped. But Rafique returned to visit her family because she thought a reconciliation was possible, police representative Ghazanfar told CNN.

The couple had known each other for five years, Khan said.

"She was unhappy, our marriage was the only way out that we had -- her family didn't approve."

'How could they be so heartless?'

Khan's mother, Shahida Khan, said that Rafique's family "had promised that not even one hair on her head would come to harm."

"We called up her uncle and he told us that they will bring her back to us themselves -- we trusted them," she said.

She said her son has been suicidal since learning of the death of his wife, whom he first met as a girl in school.

"We woke up yesterday and found out that they had burned Zeenat," she told CNN. "My son started screaming and crying. ... He said that, 'Now that she's dead, I'm going to leave this world as well.' "

The killing has left her family distraught, the mother-in-law said.

"There should be justice. How could they be so heartless and kill this girl? She was our child now; she married our son."

Rafique had also been strangled, the autopsy said, according to Geo News.

"When we saw her body, she had strangulation marks on her neck," Shahida Khan said.

Ghazanfar said investigators would need to wait for a postmortem examination to determine what Rafique had been subjected to by her killers.

Rafique's family had refused to accept her body.

Family unapologetic, police say

Ghazanfar said police were seeking Rafique's brother "because an old woman cannot perform this act alone."

"There has to be help," she said.

Punjab Chief Minister Muhammad Shehbaz Sharif was notified of the killing, Ghazanfar said.

Prime Minister Nawaz Sharif "expressed his deep concern and anguish over the killing," his office said in a statement.

He called the killing "against the values and traditions of Islam."

Shahida Khan told CNN that her family was receiving threats from Rafique's family.

The crimes originate from tribal practices and are often meted out as punishment for behavior viewed as bringing dishonor to a family or village.

CORRECTION: A previous version of this story incorrectly referred to the surnames of the victim's mother and mother-in-law. They should be identified as Parveen Rafique and Shahida Khan, respectively.