One doesn’t often associate the Islamic Republic of Iran with sex, drugs, prostitution, serial killers and detective work. But they’re all to be found in the provocative documentary “And Along Came a Spider” (6 p.m., Cinemax).

In the 12 months leading up to July 2001, Saeed Hanaei murdered 16 women in the holy city of Mashhad. After his capture, Hanaei freely admitted to the killings. He claimed that since the women were all prostitutes or drug users, he was compelled by divine will to rid society of what he called “violators of the Earth.”

A victim of Iran’s bloody war with Iraq, he felt that the fallen women were desecrating the memory of that war’s holy martyrs. During his trial, he received a lot of sympathy from religious zealots. One woman even declares that any woman who goes out without the veil and talks to men on the street is automatically a prostitute, and that the punishment for riding on the back of a man’s motorcycle should be death.

For all of his talk of piety, Hanaei — dubbed “the Spider” because he lured victims to his lair — was accused by authorities of having sex with the women before killing them. He denied this charge up until the day he was hanged.

• Laurence Llewelyn-Bowen is host of “Design Rules” (7 p.m., BBC America), a how-to series with very specific ideas about the principles of light, space, proportion and harmony. This smart and compelling series sticks to ideas as old as ancient Greece and avoids trendy and subjective notions of interior decoration.

Tonight’s other highlights

• Gibbs hunts for the terrorist who shot him on the season finale of “Navy NCIS” (7 p.m., CBS).
• Michael Douglas, Don Cheadle, Benicio Del Toro, Luis Guzman, Dennis Quaid and Catherine Zeta-Jones star in the 2000 drug-war drama “Traffic” (7 p.m., NBC), directed by Steven Soderbergh.
• The last two finalists compete on “American Idol” (7 p.m., Fox).
• The two-part miniseries “Reversible Errors” (8 p.m., CBS) concludes.
• Jack finds the last vial as Tony faces the ultimate penalty on the season finale of “24” (8 p.m., Fox).
• The trip back to the present proves difficult for residents of “Colonial House” (9 p.m., PBS).