If the Avel during Shiva comes to Shul to Daven, is Tachanun to be recited?

The Avel:[1] The Avel does not recite Tachanun during Shiva irrelevant of where he Davens.

The rest of the congregation: If an Avel is in a shul during the Shiva [and is not Davening for the Amud], some Poskim[2] rule that the congregation recites Tachanun.[3] Other Poskim[4] however rule that the entire congregation omits Tachanun just as is the law by a Chasan. [Practically, the rest of the congregation is to recite Tachanun, unless they have an accepted custom otherwise.[5] If, however, the Avel is Davening for the Amud, according to all Tachanun is omitted.[6] Likewise, if the congregation came to the Minyan in Shul specifically for the sake of the Avel, Tachanun is not recited.[7]]

___________________________________

[1] M”B 131:30; Kitzur SHU”A 22:5; Kaf Hachaim 131:60

[2] Kneses Hagedola 131:15; Elya Raba 131:9; Chayeh Adam 32:33; Kitzur SHU”A 22:5; M”B 131:30; Ketzos Hashulchan 24:7; Poskim in Kaf Hachaim 131:60

[3] The reason: As the attribute of judgment is not apparent outside of the Shiva home. [Kneses Hagedola ibid]

[4] Mamar Mordechai 131:11, brought in Kaf Hachaim

[5] Piskeiy Teshuvos 131:16; Nitei Gavriel 95:9; So is implied from Admur 131:5 who writes house of the Avel and not “and when there is an Avel in Shul” and so rules Ketzos Hashulchan ibid, however perhaps Admur ibid omitted an Avel coming to Shul being that an Avel may not leave the home; See Darkei Hachaim 21:3 regarding if the Avel is part of the ten men needed for the Minyan

[6] Gesher Hachaim 1:20-3-10 [11 in newer edition]; Piskeiy Tehsuvos ibid that so applies according to all; See Nachamu Ami 18:22; Pnei Baruch p. 115

Other opinions: Some suggest even in such a case for the Avel to remain silent while the congregation recites Tachanun and when they finish he recited kaddish. [See Mahariy Asad Y.D. 371]

[7] Nachamu Ami in name of Shenos Chaim 8; Piskeiy Teshuvos ibid; Nitei Gavriel 95:12