Yes, harming, threatening, or retaliating against retired federal law enforcement officers on account of their past official duties is a serious federal crime. [1, 2]

Under federal law, protections specifically extend to former and retired federal employees: [1, 2, 3]

• Retaliatory Actions: Under 18 U.S.C. § 115(a)(2), it is illegal to assault, kidnap, murder, or threaten a former or retired federal officer with the intent to retaliate against them for the performance of their official duties during their term of service. [1, 2, 3, 4, 5]
• Conspiracy Against Rights: If two or more people conspire to injure or threaten an individual to prevent them from exercising their federal rights, they can be prosecuted under 18 U.S.C. § 241. [1, 2, 3]
• Penalties: Simple assault on a former officer can result in fines and up to 1 year in prison. If the assault involves physical contact or an intent to commit another felony, penalties increase to 8 years in prison. If a deadly weapon is used or bodily injury is inflicted, the penalty increases up to 20 years. [1]

https://www.justice.gov/crt/statutes-enforced-criminal-section