The father of a man who admitted plotting with Al Qaeda to bomb the New York City subway system in 2009 was convicted on Friday of lying to investigators and urging others to destroy bombmaking materials to cover up evidence.

Mohammed Wali Zazi was found guilty after a three-day trial in federal court in New York. His son, Najibullah Zazi, pleaded guilty in February 2010 to attempting to carry out an Al Qaeda-ordered suicide bombing on crowded subway cars during rush hour. It never happened.

After being warned that federal agents were asking about him, Najibullah Zazi left New York and returned to his home in Colorado. That’s when his father and other family members took actions that officials say were aimed at undermining the ongoing federal investigation.

Mohammed Zazi lied to federal agents when asked if he knew an imam in New York named Ahmad Wais Afzali. The father told the agents he did not know the imam. Government officials say Mohammed Zazi, in fact, had known Afzali for years and had just spoken to him on the telephone about the federal investigation of his son. The imam had warned the Zazis of the investigation.

“This defendant sought to conceal one of the most serious terror plots in recent times,” said US Attorney Loretta Lynch in a statement. “He also enlisted others to help him spin his web of lies and destroy key evidence.”

The elder Zazi faces up to 20 years in prison on each of two charges. Najibullah Zazi faces a sentence of up to life in prison without parole.