Your statement is incorrect. The financing of armed anti-Ukrainians and Russian tourists has been going on for many weeks and has been documented. There have been intercepts of couriers from Moscow traveling from Moscow with cash and bank cards for example.
Moreover, yesterday was an instance of the Kremlin financing and arming Russian citizens and their supporters and directing them to cause mayhem and to kill people during a pro-Ukrainian demonstration. Thus, this was Russians killing Ukrainians in a Ukrainian city. It will only be a Russian city if and when Putin’s war is successful.
It is being reported in Ukrainian newspapers that the Putin had been planning a massacre of Ukrainians in Odessa on the May 9 holiday, but his timetable had to be accelerated after the attack on Sloviansk. Thus, the killing and mayhem were not as great, although many Ukrainians were shot and killed as well as injured yesterday. As for those who died in the fire, about half of those were not Ukrainian citizens and had been brought in from outside the territory of Ukraine. You should ask why there were foreigners taking an active part in an attempt to overthrow the Ukrainian government. They sound like unlawful combatants to me. Also, why did the police stand by and why was it the Ukrainian citizenry had to defend itself from these unlawful combatants?
Reports are also that most of those arrested after yesterday’s events are Russian citizens (ie, individuals from outside the territory of Ukraine). See http://www.unian.ua/politics/914211-mvs-bilshist-zatrimanih-v-odesi-gromadyani-rosiji-ta-jiteli-pridnistrovya.html
Thus, the question is why Russian citizens participating in an armed and violent action against Ukrainians in a Ukrainian city?