Well, alright, it is the BOM. :sigh:
We should probably make system.file.readFilesAsString() better at that, somehow. In the meantime, something like this should work:
bytes = system.file.readFileAsBytes("/Users/pgriffith/Downloads/Three Parameter Model Data.json")
from org.apache.commons.io.input import BOMInputStream
from java.io import ByteArrayInputStream, ByteArrayOutputStream
from java.lang import String
bomInput = BOMInputStream(ByteArrayInputStream(bytes))
outputStream = ByteArrayOutputStream(len(bytes))
bomInput.transferTo(outputStream)
bytesOut = outputStream.toByteArray()
strOut = String(bytesOut, "utf-8")
print system.util.jsonDecode(strOut)