First of all let's look at the report by Belorussian side.
eng.belta.by
Let's look at the version proposed by Polish side
wydarzenia.interia.pl
As for Western MSM then remarkably BBC-Russian and BBC-English keep silence about this story.

Polish defector: Polish border guardsmen killed volunteers at the border
Emil Czeczko said he had seen at least two situations when Polish border guardsmen shot a volunteer for asking them where they were taking refugees to.

If true then it's absolutely unacceptable. But is the statement made by the defector trustworthy? It's a big question.Polish security forces killed volunteers at the border. The Polish soldier Emil Czeczko, who had requested a political asylum in Belarus, made the statement on the air of the TV channel Belarus One, BelTA has learned.
Emil Czeczko said he had seen at least two situations when Polish border guardsmen shot a volunteer for asking them where they were taking refugees to.
Let's look at the version proposed by Polish side

Kim jest polski żołnierz, który przeszedł na stronę Białorusi? Jego wpisy w internecie mówią wiele
Emil Czeczko to żołnierz 11. mazurskiego pułku artylerii w Węgorzewie, który według informacji białoruskich mediów miał porzucić służbę w Wojsku Polskim i zbiec na Białoruś. 25-latek miał problemy z prawem i groziło mu usunięcie z armii. W przeszłości był aktywny w mediach społecznościowych...
wiadomosci.onet.pl
The Belarusian Border Committee reported on Friday that the Polish soldier asked for political asylum due to " the lack of permission for the Polish policy on the migration crisis and the practice of inhumane treatment of refugees." This is 25-year-old Emil Czeczko, a private from the 11th Masurian Artillery Regiment in the town of Wengozhevo.
The Polish side initially did not confirm the reports of the escape, reporting an "intense search action".
"The soldier who disappeared yesterday had serious problems with the law and submitted an application to leave the army. Should never be sent to serve on the border. I demanded an explanation of who is responsible for this, " Defense Minister Mariusz Blaszczak wrote on Twitter.

Wojsko reaguje na dezercję żołnierza. Zapowiada konsekwencje
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"We are dealing with an act of desertion by a citizen who until recently was a soldier of the armed forces. A man who was saved by the evil one, " said General Tomasz Petrovsky
There is an easy solution - to allow journalists, human right activists to visit the Polish side of the border and to launch an investigation in alleged wrongdoings.He said that "it is now beginning to create an image that Polish soldiers commit shameful acts prohibited by law, which is absolutely untrue. It is already clear that it comes to manipulating this young man, that he will be used in propaganda against us."
"He committed an act of desertion. Probably, it seems to him that, since the Lukashenko regime generates the criminogenic process, if the standards of compliance with the law are lowered there, it will be easier for him. Maybe he also came to the conclusion that his double game is over, because the bosses began to " see " these evil intentions of his, and in Poland, will not escape punishment ,- said General Petrovsky.
As for Western MSM then remarkably BBC-Russian and BBC-English keep silence about this story.