[10] While studying at the Moscow Theological Seminary, according to the memoirs of Hieromonk Job (Gumerov) [ru], "[Sysoev] was imbued with a fervent conviction that only Orthodoxy contains the saving truth.

The shooter (non-Russian, as noted by eyewitnesses "by his characteristic accent"), who was wearing a medical mask, also shot twice at the choir director who greeted him at the exit and fled.

Peter and Paul in Yasenevo was led by Archbishop Arseny (Epifanov) [ru] (237 priests and about a thousand laymen were present);[13] after the funeral service, Patriarch Kirill of Moscow performed a requiem lity at the coffin of the deceased.

[14][15] In his farewell speech, the Patriarch said, in particular:[16][17][18] Father Daniel did much to establish God's truth […] But, perhaps, the most powerful word he uttered is the one we are witnessing today.

[20][21] According to the main initial version of the criminal investigation, the murder was committed on religious grounds: Sysoev had previously been repeatedly threatened by representatives of an extremist group.

According to a statement made by Russian Islamists and released on kavkazcenter.com: One of our brothers who has never been to the Caucasus took up the oath of (former independent Chechen president Dokka Umarov) and expressed his desire to execute the damned Sysoyev.

[25] On 16 March 2010, Vladimir Markin, a representative of the Investigative Committee [ru], stated that on 1 December 2009, law enforcement officers shot and killed Beksultan Karybekov, a native of Kyrgyzstan, who had offered armed resistance during an arrest in Makhachkala, and confiscated the pistol with which Sysoyev was killed in November 2009.

[26] On the same day, Vladimir Vigilyansky, the head of the Patriarchate's press service, stated: "We are, of course, satisfied that there is some clarity regarding this high-profile crime.

[20][31] Sysoev spoke out on the topics of preaching Orthodoxy and performing missionary work among various groups, including skinheads,[32] Old Believers, and Muslims.

At a picket on 1 June 2009, he said: “We are here to try to defend the rights of the most defenseless citizens of our country — children killed in the womb of their mothers.