He claims she was sleeping when he left her in the trendy SoHo House hotel.
Her body was found in an overflowing bathtub with strangulation marks on her neck.
Brooks said he had nothing to do with her death and told police he never even went near the tub.
But a prosecutor said there was "no question" Brooks killed Cachay.
"They had a very intense and caring relationship and it's something he's very sad over," said Brooks' attorney, Jeffrey Hoffman.
"He has absolutely no respect for anyone at all, or the law or life or my sister or my family," said Cachay's brother, Patrick.
Brooks is being held without bail. If he's convicted he could face up to life in prison.
The Associated Press contributed to this report.