MISSOURI CITY, TX --We've got the latest developments now in the investigation into a shocking double murder. The victims include a young mother-to-be who was stabbed to death in Missouri City and her boyfriend, who was shot and killed at an apartment complex in Houston. We're learning more about the person of interest police detained in connection with the case. Police from Houston and Missouri City are still investigating the murders and are not commenting on the investigation, which leaves two families in limbo. But on Monday, a sister of one of the victims talked about the possibly motive: jealousy and money. "He was a good person -- a protector, provider, comforter," said Tarhonda Daniels, sister of Yancy Daniels. "I don't see why someone would want to kill him or the mother of his child." Tarhonda Daniels has lost her only brother, and the person being held for questioning is a cousin. Early Sunday morning, 27-year-old Leiah Jackson was stabbed nearly two dozen times in the back outside her duplex in Missouri City. She was eight months pregnant. It was to be her first child, as well as the first for Yancy Daniels, her boyfriend. The next day, his body was found at a southwest Houston apartment complex; he had been shot to death. Tarhonda Daniels believes she knows what happened. "For him to ransack the house the way he did, he knew there was something in there, some money in there," she said. Tarhonda Daniels said the family met the cousin at a family reunion about a year ago, and he moved to Houston; she says he gravitated toward her brother. "I always had an eerie feeling about him; I told my brother that he was jealous of him and I didn't trust him," she said. On Sunday, she says her fears were realized. She says the cousin asked her brother for a ride late Saturday night and that ended in Yancy Daniels' death. Tarhonda Daniels said she believes the cousin then returned to Jackson's home. "(He) lured Leiah outside and that's when he attacked her, went back in the house looking for some money," Tarhonda Daniels said. Inside his closet, clothes were found tossed about and blood was found on a storage container. That's why Tarhonda Daniels believes Jackson, her brother and their unborn son were killed that night. Tarhonda Daniels says even as the Jackson and Daniels families were desperately searching for answers Sunday, her cousin had gone to his apartment to sleep and then to her father's home to watch the Texans game. He was later arrested on unrelated charge and has been in police custody since. Tarhonda Daniels says her brother would keep what she called a couple of thousand dollars in petty cash at the home he shared with Jackson. It was money he got from composing and selling music tracks. It was everything she says her cousin didn't have and wanted. What her brother wanted most, though, was for his son to be born. "He was saying he was gonna put a baby camera in the truck," Tarhonda Daniels said. "He was so excited. He was very excited about this baby." Jackson's godmother is multiple Grammy-award winning singer Dionne Warwick. She arrived in Houston to help Jackson's family prepare for the funeral. "She was bright, tenacious; she loved life," Warwick said. "She approached life in that fashion." Jackson's funeral has been scheduled for Friday. Warwick says she has concerts in Canada on Friday and Saturday, but she is trying to find a way to attend Jackson's funeral. If she can make it, she says she may sing at the funeral. However, none of Warwick's plans have been confirmed. Services for Daniels are set for sometime next week.