Charlene Milloy, 24, held a newspaper in front of Asif Rehman and demanded: "Swear on our Adam's grave that you didn't do that to that guy." She said Rehman just shrugged his shoulders and made no reply.
Rehman, 20, and Adel Ishaq, 19, deny the racially aggravated killing of Mr McKeeney, 57, outside his home in Pollokshields, Glasgow, in January.
Miss Milloy told the High Court in Kilmarnock she knew police were searching for the pair when they turned up at her house three days after the killing.
She said: "I was getting no answer out of either of them. I think they were on some kind of drugs."
Miss Milloy asked Rehman to swear on the son they had lost together that he was innocent. After getting no reply she turned to Ishaq and asked: "What's the script?" She said: "He just shrugged as well and said, 'I didnae mean it'."
Cross-examined by Derek Ogg, QC, counsel for Ishaq, Miss Milloy admitted visiting Rehman three times in prison. She also accepted they were wed in a religious marriage but it had not been registered officially.
Miss Molloy further admitted police seized bags of diazepam and cannabis from her house in Priesthill, Glasgow, after arresting both men there.
Rehman and Ishaq, both prisoners, deny the racially aggravated murder of Mr McKeeney. They have entered special defences of incrimination, blaming each other for the killing. Rehman is said to have been on bail at the time.
The trial continues.