The Committee must subpoena Trump.
And if he refuses to show up, then they should make a criminal referral to the DOJ.
The Justice Dept needs the support of the Congress. Otherwise, it would give the other side the opportunity to attack Merrick Garland as an incompetent and reckless Attorney General.
If there is to be a "war", then it can be a battlefield for politics or for actual violence. We prefer that we resolve our differences on the political battlefield.
If Garland then makes the decision to indict Trump for various crimes, then he has the imprimatur of the people behind him, in the name of the Congress of the United States.
In my opinion, it is important that the Committee give its full support to the Department of Justice, in this instance.
It will go to the full Congress for a vote, and it will be up to each Congress person to decide which way they wish to go?
(on edit) Furthermore, they should invite him to do it publicly, but under oath. He should explain to the people his role in the attack upon our Capitol. As a former president, he should volunteer to come in and answer all questions. That is not asking too much from a former president.