Not to brag, but to explain my background.
I have studied a lot of the influence of electromagnetic radiation on the biological body.
I am very sensitive to EM-radiation like WIFI and cell phones and more.
And electromagnetic radiation was part of my major on University.
So I may know what an evil person could do with radiation.

For a radio-transmission to work:
You need an antenna system and something that reacts and amplifies the signal.
In the cells this can be the Voltage Gated Calcium Channels.
The antenna is the conducting material near the cell. And the Calcium Channels are the amplifiers.
Some people think that this is the cause of health problems with the mobile telephones.

So as evil guy, you would design a molecule that vibrates with certain frequency. Like one that 5G transmits.
Note that 5G has several operating frequencies, some lower than 4G.
But it is very similar to a local WIFI on maximum transmission.
Note that the molecule does not need to be magnetic at all to vibrate at such a frequency.
Usually these molecules get hot only, like water in a microwave.
The microwave uses the molecular vibrations of H2O.

The molecule would vibrate, but that does not do anything yet.
You also need a chemical amplifier.
So evil guy must also make the molecule start a chemical reaction while a certain frequency is being transmitted. Like a heart attack. Affecting the brain is more difficult. Maybe induce a sleep or a need for a cigarette?

This may be very complex, but for all of this no magnetic protein is required.
I think that the magnetic protein will even make it more difficult, because it will react to very low frequencies only.
In the old radios we had big spools to receive the low AM radio bands.

These molecules are complex and can probably found in autopsies.
A magnetic thing would even be easier.