John Doyle, 49, told the High Court in Edinburgh he had nothing to hide.
He described his teenage sister as "annoying but in a cute way" but admitted that in the weeks leading up to her death - more than 27 years ago - they had been growing apart.
The trial has heard Ms Doyle was found naked and strangled yards from her Greenock home early on June 2, 1986.
Mr Doyle, just short of his 22nd birthday at the time, said he was awakened by the sound of police walkie-talkies in the Ardgowan Street house.
He said: "There were two police officers in the house. My mum was running about greeting. My dad was in a state and the police were describing the circumstances of what had been going on next to the house. That a body had been found."
Mr Doyle also said he was "feeling rough" that morning. He had a hangover after drinking the night before. He told how he went with his father, who has since died, to identify Ms Doyle's body.
John Docherty, 49, is on trial and denies murder. He has given the court a list of 41 possible suspects which, he claims, might include the real culprit. John Doyle's name is one of those of those on the list.
Advocate depute John Scullion, prosecuting, asked Mr Doyle: "In the early hours of June 2, 1986, did you leave the family home?" Mr Doyle replied: "I did not." "Did you kill your sister?" the prosecutor continued. "I did not," repeated Mr Doyle.
The suggestion was ridiculous, he added.
Questioned by defence QC Donald Findlay, Mr Doyle said: "We were just normal brother and sister."
However, he added: "She was going her way and I was going mine."
The trial heard that, in a later statement to police, Mr Doyle said: "When Elaine died we weren't really talking to each other."
The statement continued: "To be frank we would disrespect each other. We would get on each other's nerves and I would see her as my annoying little sister."
Mr Doyle said that should not be taken literally. "She was annoying in a cute way," he told the trial.
The trial also heard of the "horrible coincidence" that no-one noticed Ms Doyle had not come home on the night of her death. Mr Doyle agreed his father "would go nuts" if he did not lock up after his sister before going to bed.
On a previous occasion, the trial has heard, when Ms Doyle failed to show up on time her father asked police to look for her - but not on Sunday, June 1.
Mr Doyle said that night he fell asleep: "I cannot remember locking the door that night."
Mr Findlay suggested it was "a horrible, horrible coincidence."
John Doyle told the trial he had no explanation other than coincidence.
Mr Docherty, now of Dunoon, denies murder and claims that at the time he is alleged to have stripped and strangled 16-year-old Ms Doyle he was with his parents - who are no longer alive - at their home in Greenock.
The charge alleges that, on June 2, 1986, in a lane near Ms Doyle's home in Ardgowan Street, Greenock, he seized her by the hair, struck her on the head and either removed or compelled her to remove her clothing.
The charge goes on to allege that Mr Docherty forced Ms Doyle to the ground, pushed her face into the ground, sat or knelt on the teenager then placed a ligature round her neck and strangled her.
Mr Docherty also denies stealing a handbag from Ardgowan Street on the same date.
He further denies a charge of attacking another woman, Linda Hargie, on various occasions between 1990 and 1995 at an address in Anne Street, Greenock, by seizing her and pushing her and punching her on the head.
The trial continues.