
Following the news that Russian says one of their military officers has been killed in Syria, there are now reports from opposition sources that offer a slightly different, and more plausible account.
According to the Revolutionary Forces of Syria Media Office, the officer was in fact killed not by ISIS, but by the Free-Syrian-Army-aligned Northern Division in Latakia with a US-made TOW missile, not mortars.
This would make much more sense than an ISIS attack, given that the Russian Ministry of Defence said that the officer had been helping the Syrian army familiarize themselves with new hardware. Russian military equipment is being used by regime forces primarily in the Latakia and Aleppo regions, whereas it is hard to conceive of locations along the front with ISIS, at which Russian officers would be garrisoned for this purpose.
The Syrian Local Coordination Committees (LCC) give an even more specific location - Marj Khawkha in the Jabal al-Akrad (Kurd Mountain) area.
This is just outside the town of Salma, which was captured by the regime, supported by Russian forces, in January.
The presence of Russian troops in Salma has been verified by analyses of news reports from the town:

Identification of the Russian Ground Forces in Salma, Syria - InformNapalm.org (English)
We continue to identify the Russian servicemen which execute criminal orders of the Kremlin's regime in Syria. We have already caused butthurt to the Russian officials and media by the series of publications with the personal information about the Russian pilots bombing peaceful Syrian citizens.
View full page →This makes it a very feasible area for a Russian officer to be killed in.
According to the LCC report, not one, but three Russian officers were killed, along with four officers of the Syrian army.
We also note that another rebel group, Ahrar al-Sham, released this video today which purportedly shows them targeting a "gathering of officers in the village of Marj Khawkha near Salma" with unguided rockets and mortars:
However, there is one detail about this video that is easily missed -- this is a very unique weapon that is featured in this video, one not produced in the Middle East.
Almost all of the weapons used by rebels have been captured from the Syrian regime. They are, then, Russian-made, like most of the arms in the Middle East, and ammunition is readily available as a result. This weapon, however, is different.
The rocket launcher in this video appears to be a Rak-12, a weapon that was manufactured in Croatia. The weapon is similar to the Chinese Type-63, often seen in use by both rebels and the Syria regime, but it uses different ammunition.
In 2013, before he joined The Interpreter, James Miller helped break the news that a series of Croatian weapons had landed into the hands of a newly-reorganized alliance of Syrian rebel groups. Those rebel groups appear to have been armed -- and likely trained -- by a foreign power, likely a collaboration of the American CIA, Saudi Arabia, and Qatar. One of those weapons was the Rak-12:

A rebel spokesman shows off a new weapon, possibly a Croatian Rak-12 UPDATES: This weapon has been spotted several times on the battlefield. Scroll to the bottom for details. To date, most of the insurgent arsenal in Syria has been captured from the regime's army.
View full page →Who just started arming Syria rebels?
The Council of the European Union renewed its arms embargo on Syria this week by another three months, with the slight amendment to allow for "greater non-lethal support and technical assistance for the protection of civilians."
View full page →But the ammunition for these weapons dried up in March of 2013, as the newly-formed rebel coalition captured large parts of Damascus province. The theory at the time was that Washington did not want the rebels to overthrow the regime, but instead wanted to facilitate a brokered peace.
That peace never came, and areas captured by those rebels were hit by the regime's massive chemical weapons attack just five months later.
In the last year, Syrian rebels have been using TOW anti-tank missiles, provided by the United States and its allies. In December and January, however, the supply of those missiles appeared to have dried up, and the regime advanced. Now we are once again seeing both TOW missiles, and for the first time in a long time, evidence of Croatian weapons, in use by Syrian rebels who are, by all accounts, losing territory.
-- James Miller, Pierre Vaux