A court in Mexico has denied a request by convicted drug lord Miguel Angel Felix Gallardo to serve out his sentence under house arrest due to his bad health and advanced age.

Felix Gallardo was considered the godfather of Mexican drug smuggling and a co-founder of the Guadalajara cartel. He is serving a 37-year sentence for the 1985 killing of a U.S. Drug Enforcement Administration agent.

A court ruling issued Tuesday said that just because Felix Gallardo has reached the age of 70 does not automatically qualify him for release from prison, though Mexican law allows that. The court ruled there is no compelling reason he can't be kept in prison.

Rafael Caro Quintero was also convicted in the DEA agent's murder, but was released in 2013 on jurisdictional grounds.