Thomas Warwick, the musician’s lawyer, said his client had gotten into body building and eating healthy, and later began taking nutritional supplements as a paid product spokesman. At some point, he also began taking steroids, he said. “His thought processes were devastatingly affected by his steroid use,” Warwick said.
Steroids will surely cause one to become more "angry" but I don't think to the extent of carefully plotting to kill your wife. If anything, it'd be an "in the moment" thing therefore this is an invalid excuse.