MSNBC’s Chris Matthews theorized this evening that the bombing in Boston today might be the result of a Tax Day protest – as it occurred on the deadline date for filing federal income taxes.

“As you point out, and I just forgot, I filed already. It’s filing day for the federal income tax, which does cause some emotions around the country – sometimes in the wrong parts of the brain anyway,” Matthews said during his show.

Matthews was interviewing Democratic Massachusetts Representative William Keating, who also cited tax day or Boston’s Patriots Day as a possible motive for the bombing.

Later in the program, Matthews continued to expand his theory, suggesting that the attacker could be “domestic.”

“Well, Michael, Tax Day today. That came up. You know, I was thinking of all the iconic events, or told about them today. I knew it was tax day because I got them in,” Matthews said, as he was questioning an analyst on his show.

“Would you, as an expert, be thinking domestic at this point?” Matthews continued, “I don’t think Tax Day means a lot to the Arab world or Islamic world or Al-Qaeda in terms of their world. It doesn’t have iconic significance.”