They made the mistake of being caught and now the truth will come out because they’ve all confessed (probably under threat of torture). They are Ukrainian nationals. The ISIS thing was total propaganda.
That's a lie.
Moscow terror attack: Putin says all four gunmen held as death toll reaches 133
They're Tajik and Chechen.
The group that claimed credit for the deadly terrorist attack was an Islamic State affiliate in Afghanistan called Islamic State Khorasan Province, or ISKP.
(snip)
ISKP seeks to create a caliphate across Afghanistan, Iran, Pakistan, Tajikistan, Turkmenistan and Uzbekistan.
And your point is that Russia is allowed to attack Ukraine, but Ukraine is not allowed to attack Russia?