Julian P. Heicklen, a charismatic, cantankerous chemistry professor who dedicated his retirement years to a series of public protests in defense of civil liberties, culminating in his 2011 indictment for jury tampering, died on March 11 at his home in Teaneck, N.J. He was 90.

His daughter Judith Heicklen confirmed the death but did not specify the cause.

Dr. Heicklen took on many issues, starting with civil rights in the 1960s, when he fought against housing discrimination in Los Angeles. But his highest-profile campaign was his last.

Starting in 2009, he regularly appeared in front of the federal courthouse on Pearl Street, in Lower Manhattan, demonstrating in favor of jury nullification, a controversial practice in which members of a jury who find a law unjust vote not guilty, regardless of the facts of a case, thereby nullifying the law.