Mike said he didn't feel comfortable talking about his identical twin Mark, who died on United Airlines Flight 175.

CNN: Brother of 9/11 victim speaks out after five years

Space station commander Scott Kelly, whose identical twin brother Mark Kelly is married to Giffords and is also an astronaut, led NASA in a moment of silence Monday as part of the national observance for all the victims of Saturday's shooting.

MSN: Arizona suspect could face death penalty

Denis Thatcher, father of Sir Mark, 59, and twin sister Carol, died in 2003.

BBC: Son thanks public for support after Thatcher's death