Let's look at the news release at Interfax Ukraine :
SBI opens case on Biden's pressure on Shokin – lawyer
KYIV. Feb 27 (Interfax-Ukraine) – The State Bureau of Investigations (SBI) has registered a criminal case on pressure from former U.S. Vice President Joseph Biden on former Prosecutor General of Ukraine Viktor Shokin.
"The SBI has added information on the criminal offence to the Unified Register of Pre-Trial Investigations," Shokin's lawyer Oleksandr Teleshetsky said during a press conference at the Interfax-Ukraine News Agency on February 27.
The case was opened under an appeal from Shokin. The court obliged the SBI to register the proceeding.
Read more at: https://en.interfax.com.ua/news/press-conference/643759.html
So, it does look like it comes from the Shokin camp. So it is, what it is. Yes, the gatewaypundit headline sounds like an exagerration but it also looks more like it is a "mere" probe although, again, it comes from the Shokin camp.
Now, look at this from Ukranian News:
07 February 2020, Friday, 13:46 235
Shokin’s Blood Mercury Levels Were Fatal - Treating Physician Korpan
The doctor of the Austrian clinic, Nikolai Korpan, claims that former prosecutor general Viktor Shokin was poisoned with mercury and its levels in blood were fatal.
Korpan told about this in an interview with the Ukrainian News Agency.
"Viktor Mykolayovych addressed complaints and we began to understand their cause. When we did large-scale studies, in particular, heavy metals, we got the results that the mercury levels in the blood were very high. At first we did not believe it, because the indicators point to the lethal dose. We first considered that it was some kind of technical error and having checked it was confirmed that the mercury level in Viktor Shokin’s blood was at 9.7 and we started intensive therapy,†the doctor said.
Read more at: https://ukranews.com/en/news/682633-shokin-s-blood-mercury-levels-were-fatal-treating-physician-korpan
I know, some of the Putin-media, places like Russia Today and other are reporting some of these things. I don't know if "Ukraine News" is actually Ukraine or some Russian diversion, you have to be careful. Still, if the above happened per mercury poisoning, it wouldn't be easy to totally falsify.
It doesn't quite say when this mercury poisoning occurred.